Along with the development of smaller and higher-density semiconductor devices, flip-chip mounting that uses a semiconductor chip having many bump electrodes on its surface has been drawing attention and rapidly spreading as a method for mounting a semiconductor chip on a substrate.
In flip-chip mounting, a commonly employed method for ensuring connection reliability of a bonded portion is one in which a liquid sealing adhesive (underfill) is injected into a gap between a semiconductor chip and a substrate after bonding bump electrodes of the semiconductor chip to an electrode portion of the substrate, and the adhesive is cured. Unfortunately, flip-chip mounting that uses underfill has the following drawbacks: manufacturing cost is high; underfill injection takes time; there are limitations on narrowing the distance between the electrodes as well as the distance between the semiconductor chip and the substrate; and the like.
Consequently, so-called “precoating-type flip-chip mounting” has been suggested in recent years, which includes, for example, a method for mounting a semiconductor chip on a substrate after a paste-like adhesive is applied to the substrate; and a method for mounting an adhesive-applied semiconductor chip on a substrate after a film-like or paste-like adhesive is supplied to a semiconductor wafer or semiconductor chip. In particular, the method for mounting an adhesive-applied semiconductor chip is expected to achieve a significantly shortened process because adhesive-applied semiconductor chips can be mass-produced in a lump by supplying an adhesive to a semiconductor wafer in a lump and by dicing.
However, in precoating-type flip-chip mounting, voids may result from entrapped air between the semiconductor chip or substrate and the adhesive when the bump electrodes of the semiconductor chip are brought into contact with the electrode portion of the substrate; or voids may result from a component volatilized from the adhesive during a thermal compression step when the semiconductor chip is mounted on the substrate. These voids can cause a short circuit between electrodes or cracks in the adhesive. In addition, in precoating-type flip-chip mounting, because bonding of the bump electrodes and thermal curing of the adhesive are performed at the same time in the thermal compression step, it is difficult to achieve high-precision bonding of the bump electrodes and suppression of voids at the same time.
In order to suppress voids, the following methods have been suggested, for example: a method for contracting voids by thermally curing the adhesive under a pressurized atmosphere; and a method for decreasing voids by temporarily bonding a semiconductor chip to a substrate, and then heating the temporarily bonded structure under a pressurized atmosphere (for example, Patent Literatures 1 to 3). Yet, even these methods cannot sufficiently suppress voids because air is easily entrapped due to the roughness of the substrate particularly in the case of mounting the adhesive-applied semiconductor chip on the substrate.